Ph.D., Molecular Biology, University of Pennsylvania School of Medicine
B.S., Applied Biology, Georgia Institute of Technology
Cryptococcus neoformans is an invasive opportunistic pathogen of the central nervous system and the most frequent cause of fungal meningitis resulting in more than 625,000 deaths per year worldwide. Exposure to C. neoformans is common, as it is an environmental fungus found in the soil and can enter the lungs through inhalation, leading to pulmonary infection. An increased rate of infection occurs in individuals with impaired cell-mediated immunity, particularly those with AIDS and recipients of immunosuppressive therapy. Acetate has been shown to be a major fermentation product during cryptococcal infection, but the significance of this is not yet known. We have identified three potential pathways for acetate production in C. neoformans. A bacterial pathway composed of the enzymes xylulose-5-phosphate/fructose-6-phosphate phosphoketolase (Xfp) and acetate kinase (Ack) has been identified in both euascomycete as well as basidiomycete fungi, including C. neoformans. In addition, AMP-forming acetyl-CoA synthetase (Acs), normally thought to function in the direction of acetyl-CoA formation, has been shown in Aspergillus nidulans to function in the direction of acetate production when acetylated during anaerobic growth. A third potential pathway for acetate production consists of pyruvate decarboxylase (Pdc) and acetaldehyde dehydrogenase (Ald), which has been shown to produce acetate in Saccharomyces cerevisiae during the fermentation of sugars. Each of these genes has been shown to be upregulated during infection or growth in macrophages, or under hypoxia or oxidative stress, both of which are conditions Cryptococcus would likely encounter during different phases of infection. Acetate production in C. neoformans is likely a tightly regulated process, as many of the enzymes that may be involved have been shown to be subject to post-translational regulation in other systems. We have demonstrated that C. neoformans Xfp2 is allosterically regulated by both positive and negative effectors. Ack may be modified by either phosphorylation and/or acetylation in bacteria, and Acs is regulated by acetylation. The Xfp1 homolog was identified in the Schizosaccharomyces pombe phosphoproteome, but how this phosphorylation influences activity is unknown. Pdc has also been shown to be subject to allosteric regulation and phosphorylation in S. cerevisiae. We will determine whether these C. neoformans enzymes are post-translationally modified and the effects these covalent modifications have on enzymatic activity.
T. Thaker, M. Tanabe, M. Fowler, A. Preininger, C. Ingram-Smith, K. Smith, and T. Iverson. 2013. Crystal structures of acetate kinases from the eukaryotic pathogens Entamoeba histolytica and Cryptococcus neoformans. Journal of Structural Biology 181: 185-189.
M. Fowler, C. Ingram-Smith, and K.S. Smith. 2012. A novel pyrophosphate-forming acetate kinase from the protist Entamoeba histolytica. Eukaryotic Cell 11: 1249-56.
C. Ingram-Smith*, J. Thurman, K. Zimowski, and K. Smith. 2012. Role of motif III in catalysis by acetyl-CoA synthetase. Archaea 509579. Epub 2012 Aug 15.
M. Fowler, C. Ingram-Smith, and K. Smith. 2011. Direct detection of the acetate-forming activity of the enzyme acetate kinase. Journal of Video Experimentation 58:e3474.
R. Barber, L. Zhang, M. Harnack, M. Olson, R. Kaul, C. Ingram-Smith, K. Smith. 2011. Complete genome sequence of Methanosaeta concilii, a specialist in aceticlastic methanogenesis. Journal of Bacteriology 193:3668-9.